Calcium is an essential nutrient and the most abundant mineral in the human body. Calcium plays a vital role in building healthy teeth and bones, blood clotting, muscle contraction, and nerve function. In addition to these benefits, it has recently been suggested that calcium reduces the risk of recurrence of colon polyps. see Baron J. A. et al. New England Journal of Medicine 1999; 340: 101–107. Most notably, calcium reduces the risk of bone loss caused by osteoporosis in both men and women. Despite these advantages, it has been estimated that half of all Americans do not consume sufficient amounts of calcium. More troubling, 80% of women, the group at highest risk for developing osteoporosis, do not consume enough calcium.
This deficiency is due in part to the large daily intake of calcium that is suggested by physicians. The United States Recommended Daily Allowance (“USRDA”) of calcium for adults is 800 to 1,400 mg. The National Academy of Sciences, Institute of Medicine recommends calcium intakes of 1,200 mg per day for people over 50 years of age and 1,300 mg per day for people under 19 years of age. Not surprisingly, physicians recommend calcium supplements more than any other dietary supplement.
Commercial dietary calcium supplements are typically made from natural sources of calcium carbonate, including limestone and oyster shell. Since calcium carbonate contains only 40% by weight of elemental calcium, approximately 2.5 to 3.5 g of calcium carbonate must be consumed daily to meet the recommendations. It is not practical to make tablets containing such large amounts of calcium carbonate. Consequently, supplemental calcium regimens typically comprise administering two tablets daily of 500 to 600 mg of calcium. However, even at these calcium doses, most calcium tablets are very large and difficult or uncomfortable to swallow. This problem is exacerbated when excipients are also present in the formulation. As with any solid dose pharmaceutical or nutraceutical, large tablet size often leads to poor patient compliance. In addition to calcium supplements, this disadvantage is commonly encountered with tablets having large amounts of active ingredients, such as multi-vitamins and high-dose pharmaceuticals.
Prior approaches for reducing tablet size include increasing the compaction pressure during tableting and reducing the dose of some or all of the active ingredients in a tablet. There are disadvantages associated with both of these approaches. For instance, high compaction pressures during tableting may result in brittle tablets that are prone to breaking. Further, disintegration and dissolution characteristics of tablets may be affected by compaction pressure, altering the bioavailablity of the active ingredient. Reducing the quantity of one or more active ingredients per tablet requires more tablets to be consumed to achieve a required dosage or, as in the case of some multi-vitamins, results in deficiencies of selected active ingredients. For example, most commercial multi-vitamin tablets provide only 10 to 20% of the USRDA recommended dose calcium. It is necessary to reduce the levels of calcium in these tablets in order to accommodate higher levels of other vitamins.
Calcium carbonate tablets, like other pharmaceutical and nutraceutical tablets, are prepared by the application of pressure to solid formulations. Some powdered formulations inherently possess the necessary cohesive and flow properties required for compression. Like most powders, however, calcium carbonate lacks the ability to be directly compressed and must be converted into a form more suitable for tableting through a process known as granulation.
Generally, the granulation process involves treating dry powders with agents that increase the adhesive properties of the particles resulting in stable agglomerations of the powder particles. Granulation methods known in the art include wet granulation, dry granulation, and fluid bed granulation. Of these, wet granulation is the most widely used method. In wet granulation, the dry powder components are blended in a suitable mixer followed by addition of a binding agent and further mixing to achieve the desired consistency. After drying, the granulated compositions typically have a free flowing, sand-like texture. Granulation provides the required cohesiveness and compactability for compression into tablets of satisfactory hardness and friability.
There is a continuing need for granulations that are highly compactable. Accordingly, it is an object of the invention to provide granulations that can be compressed into smaller tablets than those known heretofore. Further, it is an object of the invention to provide formulations and processes for preparing granulations.